LOS ANGELES — If you’re wondering whether a Democratic wave could wash away the current GOP-controlled Congress in November, check out what’s happened so far this week in the traditional Republican stronghold of Orange County, Calif.

Two short days ago, the situation was stable. Four congressional districts overlap with the O.C.; Republicans represent all four. Each of these Republicans (Ed Royce in CA-39, Darrell Issa in CA-49, Dana Rohrabacher in CA-48, Mimi Walters in CA-45) was considered vulnerable to some degree, in part because in 2016, Hillary Clinton defeated Donald Trump in their districts — a first for a Democratic presidential candidate. But thanks to the power of incumbency and a few big war chests, the Washington consensus said that only Rohrabacher’s race was a tossup. The rest still leaned Republican.

What a difference 48 hours makes.

On Tuesday morning, Royce, the powerful chairman of the House Foreign Affairs Committee, stunned the political world by announcing his retirement. “In this final year of my Foreign Affairs Committee chairmanship, I want to focus fully on the urgent threats facing our nation,” Royce said in a statement. “With this in mind, and with the support of my wife, Marie, I have decided not to seek reelection in November.

Then, one day later, Issa followed Royce out the door. “Throughout my service, I worked hard and never lost sight of the people our government is supposed to serve,” Issa said in a statement. “Yet with the support of my family, I have decided that I will not seek reelection in California’s 49th District.”

In response, the authoritative handicappers at the Cook Political Report flipped bothseats from Lean Republican to Lean Democrat, improving the Dems’ odds of picking up the 24 seats they need to take back the House.

Democrats, of course, rejoiced. “The Republican agenda in Washington has been a direct attack on Californians,” crowed Drew Godinich, a spokesman for the Democratic Congressional Campaign Committee. “California Republicans clearly see the writing on the wall and realize that their party and its priorities are toxic to their reelection chances in 2018.”

But beyond the predictable partisan messaging, what does this week’s sudden upending of some of the most important House contests in the country actually say about the looming 2018 midterms?

First, the DCCC may have a point. “Toxic” may be too strong a word, but there has been a real conflict between the priorities of the GOP leadership in Washington — both on Capitol Hill and in the White House — and the electoral interests of blue-state Republicans.

Take 2017’s two defining legislative efforts: Obamacare repeal and tax cuts. The former, which never passed the Senate, was wildly unpopular in California, where residents have flocked to the state-run health insurance exchange. Yet both Royce and Issa felt compelled to vote for it, despite near-constant protests from activists in their districts.

The Trump tax cuts, meanwhile, inspired even more Golden State outrage, largely because they slashed deductions for mortgage interest and for state and local taxes, which disproportionately benefit Californians. Both Royce and Issa publicly struggled to get to yes on the bill; eventually, Royce did, and Issa — gun-shy after securing reelection in 2016 by a mere 1,600 votes — did not. But their constituents know that what really matters is which party controls the House, and the national GOP agenda isn’t working to the advantage of most Republicans in California — or high-tax states such as New York and New Jersey either.

This tension has, in turn, underscored the deeper Trump-era challenges facing Royce, Issa and their ilk. Clinton won Orange County — a place that had been the heart of the conservative movement, fueling the campaigns of Barry Goldwater and, later, Ronald Reagan — for two reasons (as I’ve written in the past).

In recent years, the local Asian population has surged as well. The result is a region that’s much more diverse, and much more reliant on immigrants, than it was in Reagan’s day.

At the same time, the white voters who still make up a plurality of Orange County’s electorate are, for the most part, a particular breed: wealthier and more educated than average.

Which brings us to the second force at work here: Donald Trump. In 2016, the New York developer underperformed among white college graduates, and lost college women to Clinton by 7 percentage points. Combine that weakness with Trump’s widespread unpopularity among Latinos and other minorities, and you start to see why Trump lost Orange County by 9 percentage points only four years after Mitt Romney won there by 6. He was a particularly bad fit for its evolving electorate — and now that he’s president, his 39 percent approval rating and anti-blue-state policies probably aren’t helping matters. (The Trump administration’s decision to allow oil companies to resume offshore drilling — and then to exempt Florida but not California — angered Californians who may still remember disastrous spills off their beaches.)

All of which has conspired to make reelection more of a slog for Issa, Royce and other suburban and/or blue-state Republicans nationwide — and to make retirement sound more appealing. The numbers tell the tale. As NPR’s Jessica Taylor has noted, there are now “31 Republicans who will not seek reelection in November: 19 who are retiring outright and another 12 who are running for higher office.”

The last time either party had nearly that many members vacate their seats during a midterm year was 1994. Twenty-eight Democrats departed that cycle — and the GOP eventually took control of Congress, gaining a staggering 54 House seats in what was billed at the time as a “Republican Revolution.”

So yes, the back-to-back retirements of Royce and Issa are symptomatic of something larger: an electoral landscape that is rapidly shifting in the Democrats’ favor.

This sort of momentum wouldn’t matter much if the Dems weren’t prepared to capitalize on it. But so far, they seem to be.

Six Democratic candidates are already running for Royce’s seat, including Mai-Khanh Tran, a Vietnam-War-refugee-turned-pediatrician-turned-two-time-cancer-survivor; Andy Thorburn, a teacher-turned-union-leader-turned-millionaire-businessman; and Gil Cisneros, a Navy veteran and former shipping manager who became a philanthropist after winning a $266 million lottery prize in 2010.

And four Democrats are gunning for Issa’s job: environmental activist Mike Levin, who’s raked in more than a million dollars since announcing his candidacy in March; Sara Jacobs, a former Obama administration official endorsed by EMILY’s List; Paul Kerr, a real estate investor who outraised Issa last quarter; and Doug Applegate, a Marine veteran and attorney who nearly defeated Issa in 2016 in that cycle’s closest congressional contest.

In other words, these are not the gadflies, vanity candidates and sacrificial lambs that have tended to run against Royce & Co. in previous elections.

But before Democrats get too excited, a note of caution. This cycle’s unprecedented glut of Trump-resisting recruits could be a mixed blessing — particularly in California, and particularly in contests without a GOP incumbent on the ballot.

The Golden State, you’ll recall, has a nonpartisan primary system: Democrats, Republicans and independents all compete against each other in the primary, and the top two finishers proceed to the general election regardless of party affiliation.

Here, the risk is that splitting the Democratic vote four or six ways in a historically conservative area could allow two Republican candidates to come out on top — a result that becomes more likely when a GOP incumbent is no longer monopolizing the Republican vote and a couple of serious Republicans step in to replace him or her.

Which is probably what will happen now that Royce and Issa are gone. Though the California GOP has been decimated statewide, the party’s infrastructure remains strong in Orange County. Well-known candidates are already volunteering to run in Royce’s place, including former assemblywoman and longtime former Royce aide Young Kim, whom Royce immediately endorsed. Also in the mix are former state Senate Minority Leader Bob Huff and Orange County supervisor Shawn Nelson.

New Republican candidates are expected to announce soon in Issa’s district, where top names include state assemblyman Bill Brough, who has said he’s “considering running”; Diane Harkey, chair of the California Board of Equalization, which administers taxes and fees; and Scott Baugh, a former Orange County GOP chairman.

None of these Republicans will have incumbent-level name ID — or cash. But they also won’t have congressional voting records, which means they’ll be able to put more space between themselves and the national GOP (and Trump) than any incumbent.

The bottom line is that by announcing their retirements in quick succession, Royce and Issa have emphasized how everything is set to break the Democrats’ way in 2018. But riding a wave to victory next November will require skill and strategy and maybe a bit of luck — and now more than ever, Orange County is the place to watch to find out if the Democratic Party can pull it off.